International Myeloma Working Group (IMWG) Criteria for the Diagnosis of Multiple Myeloma

The updated criteria for the diagnosis of myeloma represent a paradigm shift in the approach to myeloma and have considerable impact on the management of the disease.

For decades the diagnosis of multiple myeloma required the presence of end-organ damage known as the CRAB criteria, including increased calcium level, renal dysfunction, anemia, and destructive bone lesions. The updated criteria allow for treatment of patients who are at such high risk of progression to symptomatic disease that it is clear they would benefit from therapy—and also potentially live longer—if they were treated before serious organ damage occurred.

The revised IMWG criteria allow, in addition to the classic CRAB features, three “myeloma defining events” (MDEs). The presence of at least one of these markers is considered sufficient for a diagnosis of multiple myeloma, regardless of the presence or absence of symptoms or CRAB features. Each of these markers has been shown in two or more independent studies to be associated with an approximately 80% or higher risk of developing myeloma-related organ damage within two years.

The new definition of active multiple myeloma is:

Clonal bone marrow plasma cells ?10% or biopsy-proven bony or extramedullary plasmacytoma and any one or more of the following CRAB features and myeloma-defining events:

Evidence of end organ damage that can be attributed to the underlying plasma cell proliferative disorder, specifically:

Anemia: hemoglobin valure of >20g/L below the lowest limit of normal, or a hemoglobin value <100g/L

Bone lesions: one or more osteolytic lesion on skeletal radiography, CT, or PET/CT. If bone marrow has <10% clonal plasma cells, more than one bone lesion is required to distinguish from solitary plasmacytoma with minimal marrow involvement

Any one or more of the following biomarkers of malignancy (MDEs):

60% or greater clonal plasma cells on bone marrow examination

Serum involved / uninvolved free light chain ratio of 100 or greater, provided the absolute level of the involved light chain is at least 100mg/L (a patient’s “involved” free light chain—either kappa or lambda—is the one that is above the normal reference range; the “uninvolved” free light chain is the one that is typically in, or below, the normal range)

More than one focal lesion on MRI that is at least 5mm or greater in size.

The IWMG now recommends the use of low-dose whole-body CT (LDWBCT) or MRI in the work-up of smoldering multiple myeloma (SMM) and solitary plasmacytoma.

The IMWG now recommends that one of PET-CT, LDWBCT, or MRI of the whole body or spine be done in all patients with suspected smoldering myeloma, with the exact imaging modality determined by availability and resources.

Clear evidence of one or more sites of osteolytic bone destruction (?5mm in size) seen on CT (including LDWBCT) or PET-CT does fulfill the criteria for bone disease in multiple myeloma, and should be regarded as meeting the CRAB requirement irrespective of whether the lesions can be visualized on skeletal radiography or not.

Increased uptake on PET-CT alone is not adequate for the diagnosis of multiple myeloma; evidence of underlying osteolytic bone destruction is needed on the CT portion of the examination.

Bone densitometry studies are not sufficient to determine presence of multiple myeloma.

The IMWG no longer recommends the presence of osteoporosis or vertebral compression fractures in the absence of lytic lesions as being sufficient evidence of bone disease for purposes of the diagnostic criteria.